Why is the dynasty with Chang 'an as its capital strong and Luoyang as its capital weak?

Qian Mu believes that Chang 'an represents external temperament and Luoyang represents internal temperament, which directly affects the national luck; Secondly, Chang 'an is in the letter, and eight rivers, such as Weishui, pass through the territory, backed by Qinling Mountains and Bashu, making it the first place of geomantic omen in China. Luoyang, on the other hand, is located on both sides of the Luoshui River and the Yellow River, surrounded by enemies. If the northern nomads break through the Great Wall, they can wipe out the capital, so it is not a good place to build a country. And so on, and so on, various factors caused the difference between the two dynasties.